Colorectal cancer (CRC) incidence continues to rise in younger adults, with no signs of plateauing, according to investigators who recently conducted an analysis of a large US cancer registry.

Adults aged 50 years and younger accounted for about 12% of colorectal cancer diagnoses in 2015, up from 10% in 2004, and significantly more of those younger patients had advanced disease at diagnosis as compared to older adults, according to the analysis of the National Cancer Database (NCDB) by Boone Goodgame, MD, of the University of Texas at Austin, and colleagues.

“These results may provide support for adjusting CRC screening guidelines to identify patients before the age of 50 years,” said Dr. Goodgame and study coauthors in Cancer.

Only 5.8% of colorectal cancer cases were diagnosed in individuals younger than 45 years, suggesting that age may be an “appropriate target” for the screening age, the authors said in their report, alluding to the 2018 qualified recommendation from the American Cancer Society to begin screening at age 45.

However, a member of the U.S. Preventive Services Task Force – which continues to recommend screening of asymptomatic adults starting at 50 years – said in an editorial that it remains “unknown” whether the harms of screening for sporadic cases of colorectal cancer in younger individuals would outweigh the benefits.

The study by Dr. Goodgame and colleagues included a total of 1,185,763 colorectal cancer cases in the NCDB during 2004-2015, of which 89% were diagnosed at the age of 50 or older, and 11% were diagnosed in younger individuals.

The proportion of colorectal cancer cases diagnosed in people aged 50 years and younger increased from 10.0% to 12.2% during the study period (P less than .0001), with comparable increases for both rectal and colon primary tumors, according to the the journal article.

Younger patients were more likely to have stage III and stage IV disease than older patients were, according to the investigators. Stage III disease was reported for 28.1% and 23.1% of younger individuals and those over 50 years, respectively, while stage IV disease was reported for 23.5% and 16.9% (P less than .0001 for both comparisons).

Race and sex differences were seen in proportions of patients younger than 50 years with colorectal cancer, further analysis of the NCDB data showed.

Among men, only non-Hispanic whites had a significant increase in colorectal cancer diagnoses under the age of 50 years over the study period, while in women, significant increases were seen in Hispanic and non-Hispanic whites, according to the report.

It’s unclear exactly what’s behind the increase in colorectal cancer diagnosis, the authors acknowledged in their report, citing a host of potentially explanatory factors, such as access to health care, lifestyle factors such as obesity, or increased antibiotic use.

Some say the increase could simply be from the more liberal use of colonoscopy, resulting in a lead time bias, the authors noted.

“However, a change in the lead-time bias should also increase the proportion of earlier stage disease in younger adults, and we did not see this in our study,” they said in the report. “Therefore, increasing colonoscopy use does not appear to be a sufficient explanation for this association.”

In any case, more studies are needed to better determine the risks, benefits, and costs of screening individuals younger than 50 years for colorectal cancer, they concluded, saying that their data should be included in an “ongoing discussion” of screening guidelines.

Dr. Goodgame and coauthors made no conflict of interest disclosures related to the study, which was supported by the National Cancer Institute and the Cancer Prevention and Research Institute of Texas.

SOURCE: Virostko J et al. Cancer. 2019 Jul 22. doi: 10.1002/cncr.32347.